Mass spectroscopy

Question 1

Describe the relationship between kinetic energy and speed

Answer 1

If speed increases then kinetic energy also increases.

Question 2

Describe the relationship between kinetic energy and mass.

Answer 2

The higher an objects mass, the slower it moves, given it has the same kinetic energy.

The greater an objects mass the greater its kinetic energy.

Question 3

what is the formula for kinetic energy?

Answer 3

1/2 x m x V2

Question 4

what are the unit of kinetic energy?

Answer 4

Joules (J)

Question 5

What type of mass spectrometer is used at A level?

Answer 5

A time of flight mass spectrometer.

Question 6

how many stages does a mass spectrometer have?

Answer 6

4

Question 7

Name each stage of the mass spectrometer in order

Answer 7

1. Ionisation.
2. Acceleration.
3. Ion drift.
4. Detection.

Question 8

Describe ionisation ( electron impact ionisation) stage.

Answer 8

Ionisation means tuning an atom into an ion.

first, atoms are heated up to separate them from one another, this is known as vaporisation ( they are vaporised).

Then you fire an electron gun at the atoms, which fires electron at the atoms, thus knocking down electrons from the atom, which in turn causes it to become a positively charged ion, ready for the acceleration stage.

Question 9

Describe acceleration stage.

Answer 9

The ion is accelerated by giving it some kinetic energy. There is an electrically charged negative plate, which attracts positive ions.

The ions are accelerated by this plate, thus causing them to gain speed and kinetic energy.

Because we know how strong the negative charge plate is and how strong the charge of the atom is, we can work out exactly how much kinetic energy the ions get.

Question 10

explain why all ions have the same kinetic energy in the acceleration stage.

Answer 10

Its because the size of the ion doesn’t determine the KE of the ion, but rather it’s charge determines how much KE it receives.

Question 11

Describe the ion drift stage.

Answer 11

This stage involves the flight tube. The ions now drift at a constant speed. The flight tube needs to be a vacuum, meaning that there is no air inside.

If there would be air, then the ion, would slow down due to air resistance, meaning that the ons wouldn’t drift.

A vacuum is achieved by sucking all the air out.

Question 12

describe the detection stage.

Answer 12

At the end of the mass spectrometer, there is a metal plate ( detector), which contains delocalised electrons.

The ions then pick up these delocalised electrons, thus turning into atoms.

This movement of electrons creates an electrical current, which is then detected and interpreted by a compiter.

Question 13

why is it important to ionise ions?

Answer 13

1. So that they can be accelerated by an electrical field ( negatively charged plate).
2. so that the ions can pick up electrons at the detector, nd thus form a current.

Question 14

Why is it important to have a vacuum in a flight tube?

Answer 14

1. So that the ions can travel at a constant speed.

Question 15

what do we use to determine the mass of an atom in mass spectrometer?

Answer 15

we measure the time taken to reach the detector.

Question 16

what do we use to determine the number of atoms of a particular mass in a mass spectrometre?

Answer 16

The size of the current.

Question 17

What is the mass spectra?

Answer 17

once lots of ions have been recorded, the computer does its calculations and gives out a diagram.

Relative abundance(%) on Y axis, and mass/charge ratio on X axis.